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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.lang.c
Subject: Re: Absolute addressing in Turbo-C
Message-ID: <27188@sun.uucp>
Date: Thu, 3-Sep-87 15:00:40 EDT
Article-I.D.: sun.27188
Posted: Thu Sep  3 15:00:40 1987
Date-Received: Sat, 5-Sep-87 12:16:46 EDT
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> It's this: Just WHY is it in C 'better' to write: *(a+n) instead of: a[n],
> where 'a' is an array of something? And how much 'better' is it?

It isn't any "better"; in fact, it's exactly the same.  "a[n]" is defined as
"*(a+n)".

The only ways in which one would be "better" would either be that one is
somehow stylistically, or that one generates better code.  Different people
have different preferences in style, and different compilers may well not
always generate better code for the same version (our compiler generates the
same code for both of them), so it's not clear there is a single style that
could be considered "better" in any objective sense.

> I remember reading on this list some time back that this does not extend to
> arrays of more than one dimension. Why? Just because the expressions will
> get too complex?

No, this extends quite well to arrays of more than one dimension: "a[i][j]" is
(a[i])[j], and thus is *((*(a+i)) + j).  There may be some confusion because
"*(a+i)" is an array-valued expression, and K&R doesn't discuss this notion;
however, ANSI C does - array-valued expressions, in most contexts, are
converted to pointer-valued expressions whose value is a pointer to the first
element of the array.  This is the obvious generalization of the K&R rule that
the name of an array, in most contexts, is converted to a pointer to the first
member of that array; this generalization is implemented by our C compiler, and
probably by most if not all other PCC-based compilers and most likely by many
other compilers as well.
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com